I also find it very effective after a long day, when my body is tired but the mind is still over-active.
It calms the brain and helps relieve mild depression.
It also stretches the spine, shoulders, hamstrings, and groins. It stimulates the liver and kidneys, relieves anxiety, fatigue, headache.
It's therapeutic for high blood pressure, insomnia, and sinusitis.
You should hinge from the hips, not the waist. Make sure that the spine is long and straight, as you don't want to exacerbate the curve of your spine. If you can't comfortably reach the extended-leg foot, sit on a folded blanket, or use a strap.
Don't sacrifice comfort in an attempt to bring your head to the knee. Rest your head on a chair and a cushion and you will still get all the benefits of this pose.